Variable speed pulley systems are used for transmitting power from one location to another in applications requiring an adjustable drive ratio between a drive shaft and a driven shaft. The pulley systems are typically powered by an engine or other drive mechanism. As conventionally known, variable speed pulley systems may be used to drive a multitude of secondary mechanisms for performing a variety of different functions.
Variable speed pulley systems usually include a drive pulley, a driven pulley, and a belt. The drive pulley generally comprises two pulley plates, one of which is anchored and the other of which is movable with respect to the anchored pulley plate. The belt extends from between these two plates on one end to some distal pivot, which may be another sheave comprising two spaced apart pulley plates and a torque sensing unit for accommodating fluctuating loads. The torque sensing unit, as described in U.S. Pat. No. 4,173,155 issued to Togami et al, reacts to a quick change in the load applied by the belt (for example, in response to a large mat or quantity of material entering a threshing mechanism).
Each pulley plate of the drive and driven pulleys has a face that encompasses a pulley contact surface. The pulley contact surfaces of two pulley plates of either the drive or driven pulley face one another. The pulley contact surfaces are generally angled so that as the distance between the pulley plates is reduced, the belt is forced into contact with the faces of the plates at a greater spacing from the center of the faces. Conversely, as the plates are moved apart, the belt is allowed to contact the faces of the plates at a smaller spacing from the center.
Many of the machines employing a pulley system as a component, such as agricultural and construction equipment, are subject to large amounts of dirt, dust and chaff which fills the air and becomes deposited upon the pulley plates and the belt. This problem is of special concern in harvesting machines such as combines where the harvesting machine itself generates a large volume of chaff during the harvest of crops. The dirt, dust and chaff which become deposited upon the pulley plates reduce the coefficient of friction between the pulley plates and the belt causing the belt to slip and heat up. As a result, the dust, dirt and chaff deposited upon the pulley plates and the belt reduce belt life and reduce power transmission efficiency. Variable speed pulleys and pulleys used in conjunction with torque sensing devices have an additional problem in that the engagement between the pulley plates and the belt occurs over a small surface area. Consequently, even in a clean environment, it is desirable to increase the friction between the plates and the belt in order to achieve greater power through-put values.
Thus, there is a continuing need for a device that removes debris from the belt and increases the friction between the pulley plate and belt of a pulley system without requiring dismantling of the pulley system.